iwlwifi: dbg_ini: fix memory leak in alloc_sgtable

In alloc_sgtable if alloc_page fails, the alocated table should be
released.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>